Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 9: Intermetallic Phases I

MM 9.3: Talk

Monday, March 23, 2009, 15:15–15:30, IFW B

Structural stability of topologically close-packed phases in transition metals — •Thomas Hammerschmidt¹, Bernhard Seiser², Ralf Drautz¹, and David G. Pettifor² — ¹ICAMS, Ruhr-University Bochum, Bochum, Germany — ²Department of Materials, University of Oxford, Oxford, UK

The formation of topologically close-packed (tcp) phases in Ni-based superalloys leads to the degradation of the creep properties of the alloys. The precipitation of the tcp phases is attributed to refractory elements that are added in low concentration to improve creep resistance. We have compiled a structure map of the occurrence of tcp phases in binary transition metal (TM) compounds. The structure map displays well-established structural trends that are driven by the d-band filling. It also shows that different sizes of the elements tend to stabilize the Laves phases over other tcp phases. The same trend is reproduced in our extensive density functional theory (DFT) calculations of the tcp phases A15, C14, C15, C36, µ, σ, and χ. We show that the structural trend can be understood using the canonical d-band tight-binding model. The small positive values of the heats of formation of all tcp phases suggest that entropy plays a key role in the stabilization of the experimentally observed tcp phases in TM binary compounds.